VolcanoesFormation, Risks and Opportunities

Volcanoes• Why do some places

have volcanoes and not others?

• Are all volcanoes the same? What are the

differences?• Are all volcanoes deadly?• Despite the risks, why do

so many people chose to live near to volcanoes?

Definition:

A conical mountain or hill, having a crater through which lava, rock fragments, hot vapor, and gas erupts.

Three volcanoes of southern Chile from the air: Villarrica (prominent peak in the foreground), Quetrupillan (snow-covered region in the middle ground) and Lanin (snow capped peak in the distance).

Japan Self-Defense Force soldiers and firefighters work among mountain lodges covered with volcanic ash near the peak of Mount Ontake on September 28, 2014.

An undersea volcano is seen erupting off the

coast of Tonga, March 18, 2009

The Aleutian Islands are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the United States and Russia.

The Aleutian Islands, aerial view

Describe the distribution of volcanoes around the world

Why so many?• Majority of the plate

boundaries here are CONVERGENT boundaries.

• COMPRESSIONAL and DESTRUCTIVE nature of the plate movements here

• = more fractures found along the crust

• + the crust here is more BRITTLE (see explanation next slide)

SubductionOceanic Continental

When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench.

This plate, as it is subducted, releases water into the base of the over-riding plate, and this water mixes with the rock, thus changing its composition causing some rock to melt and rise.

Indonesia has the most volcanoes in any one country. 127 active and 23 inactive.

Refer to Fig. 1.38, p.26

Refer to p.27 to 28• Compare and contrast Figure 1.41 and Figure 1.43• Slope/gradient?• Materials?• Eruption intensity?• Openings?• Example?

Shield VolcanoMauna Loa Volcano, Hawaii

Less violent eruption

Gently sloping

Broad base

Formed by lava low in viscosity= Lava spreads over a large area= Lava cools and solidifies slowly

Hawaiian Eruption

Steep slopes at the top

Formed by lava high in viscosity= Lava spreads over a small area before solidifying

Gentle slopes towards the bottom

CONCAVE PROFILE

Composite VolcanoMt Rainier, Washington

Erupts violently• Pyroclastic flows• Lahars / mudflows• Huge ash clouds• Lava flows

Aniakchak Caldera, Alaska, United States

Formation of a Caldera1

2

3

4

5

See: https://www.youtube.com/watch?v=gQRt2NCmEw8

Mount Katmai, Alaska, United States

What about hotspots?

Hotspot Volcanoes

Hotspot at Hawaii

Places known as hotspots or hot spots are volcanic regions thought to be fed by

underlying mantle that is anomalously hot compared with the surrounding mantle.

They may be on, near to, or far from tectonic plate boundaries. 

Difference betweendivergent plate boundary?

• The magma plumes found at a hotspot stay ‘fixed’ and do not move, regardless of the movement of the plates.

• The magma plume found at a divergent plate boundary is tied to the movement of the plates and moves along side it.

Divergent Boundary

Hotspot

Despite the risks…Why do millions of people continue to live near volcanoes?

Living with Volcanoes (p.39-42)Risks Benefits Destruction and death

by: Volcanic materials Landslides

Disruption of way of life

E.g. air planes grounded for days/weeks

Villages wiped

Fertile soils Minerals and

precious stones Tourism Geothermal energy

2010 Eruptions of

Mount Merapi

353 people were killed during the eruptions, many as a result of pyroclastic flows.

Rescuers search for victims of the Mount Merapi eruption

Yet despite the risks…

Others: Tourists at Kilauea on the Big Island of Hawaii

Others: Volcanic diamonds – not just jewellery!

The applications for diamonds are diverse and plenty 

Others: Geothermal plants in Iceland